Reaction of silicon with air

The surface of lumps of silicon is protected by a very thin layer of silicon dioxide, SiO2. This renders silicon more or less inert to further oxidation by air even up to about 900°C. After this, reaction with oxygen in the air gives silicon dioxide. At temperatures above about 1400°C, silicon reacts with nitrogen, N2, in the air as well as oxygen, to form the silicon nitrides SiN and Si3N4.

Si(s) + O2(g) → SiO2(s)

2Si(s) + N2(g) → 2SiN(s)

3Si(s) + 2N2(g) → Si3N4(s)

Reaction of silicon with water

The surface of lumps of silicon is protected by a very thin layer of silicon dioxide, SiO2. This renders silicon more or less inert to water and even steam.

Reaction of silicon with the halogens

Silicon reacts vigorously with all the halogens to form silicon tetrahalides. So, it reacts with fluorine, F2, chlorine, Cl2, bromine, I2, and iodine, I2, to form respectively silicon(IV) fluoride, SiF4, silicon(IV) chloride, SiCl4, silicon(IV) bromide, SiBr4, and silicon(IV) iodide, SiI4. The reaction with fluorine takes palce at room temperature but the others requiring warming over 300°C.

Si(s) + 2F2(l) → SiF4(g)

Si(s) + 2Cl2(l) → SiCl4(g)

Si(s) + 2Br2(l) → SiBr4(l)

Si(s) + 2I2(l) → SiI4(s)

Reaction of silicon with acids

Silicon does not react with most acids under normal conditions but is dissolved by hydrofluoric acid, HF, a reaction apparently deiven by the stability of the Si(IV) fluoride complex [SiF6]2-.

Si(s) + 6HF(aq) → [SiF6]2-(aq) + 2H+(aq) + 2H2(g)

Reaction of silicon with bases

Silicon is attacked by bases such as aqueous sodium hydroxide to give silicates, highly complex species containing the anion [SiO4]4-.